Systems for supplying fuel and fuel/air mixtures to internal combustion engines have long been known and are well developed. It is possible to characterize an internal combustion engine according to the manner in which the fuel is delivered to the inlet manifold of the engine. In many cases the engine is normally aspirated, that is using the low pressure or partial vacuum generated by the descending piston of the engine to draw fuel or a mixture of fuel and air into the cylinder. The amount of fuel fed to the engine and the flow of fuel/air mixture is typically regulated on such engines using a throttle or carburetor.
As an alternative to the normally aspirated fuel supply system, fuel injection systems have been developed and are now commonly employed on internal combustion engines operating with normally liquid hydrocarbon fuels, such as gasoline and diesel. In a typical fuel injection system, the normally liquid fuel is injected under pressure into the cylinders of the engine at the appropriate time during the combustion cycle.
One particular class of internal combustion engines are low speed, two cycle internal combustion engines powered by normally gaseous hydrocarbon fuels. Such engines typically operate at speeds below 1000 rpm, often in the range of from 250 to 500 rpm. The normally gaseous hydrocarbon fuels combusted by these engines include natural gas, associated gas, and refinery gas, as well as sour gas, such as produced from waste sites and sewerage treatment plants. The normally gaseous fuel is fed wider pressure by a fuel supply system to the inlet manifold of the engine. The flow rate of the fuel, and hence the operating speed of the engine, is regulated by a throttle assembly. An example of such engines is the Ajax™ range of engines available commercially from Cooper Cameron Corporation.
During operation of any internal combustion engine, it is important that the integrity of the fuel supply system is maintained, in order to avoid leakage of fuel. This is important to avoid potentially hazardous situations developing from the build up of combustible and potentially explosive concentrations of the fuel in the air surrounding the engine. It is also important to prevent fuel leakage from any part of the engine for environmental reasons. To this end, it is essential that any joint or connection in the fuel system is properly assembled and sealed, so as to retain the fuel within the system. Various types of sealing arrangement have been employed. One of the most common sealing arrangement is to form joints or connections in the fuel system using mating flanges, between which is sandwiched a gasket of a suitable sealing material. The flanges are fastened together, typically using bolts, to compress the gasket sufficiently to form the requisite seal. Such gasketed joints are amongst the most common form of joint in internal combustion engines and find widespread use, in particular in normally aspirated engines.
Engines operating with a fuel injection system may require an alternative sealing arrangement to be employed, in order to prevent fuel escaping. In particular, it is known to employ o-rings to seal the injectors of fuel injection systems into the respective bore in the cylinder head. The o-ring functions to seal the injector element into the bore and prevent fuel escaping from the cylinder, when under compression.
Thus, U.S. Pat. No. 4,307,693 discloses a fuel injection installation for internal combustion engines, in which injection valves for supplying fuel to the engine are sealed to either the intake manifold of the engine or to the cylinder head by at least one o-ring. The ring is braced only in the radial direction. In the arrangement disclosed, the o-ring is compressed between a first surface on the injector valve and a second surface formed in the bore in the manifold or cylinder head, both the first and second surfaces being parallel to the direction of flow of the fuel within the injection valve. It is specifically noted in U.S. Pat. No. 4,307,693 that longitudinal or axial bracing of the o-ring is to be avoided.
Similarly, U.S. Pat. No. 4,647,012 discloses an injection valve for an internal combustion engine, in which the valve is retained in a bore in the suction pipe or manifold by a sealing ring or o-ring. As with U.S. Pat. No. 4,307,693, the o-ring is retained between two surfaces one each formed on the injection valve and the bore and is subjected to a radial compression force. U.S. Pat. No. 4,307,693 discloses a chamfered collar for use in the insertion of the injection valve in the bore, in order to avoid damage being caused to the o-ring.
U.S. Pat. No. 5,752,487 similarly discloses the use of an o-ring to seal an injector in a cylinder head. The o-ring is retained in a groove and subjected to a radial compression against the surface of the bore into which the injector is installed. The o-ring is not subjected to an axial or longitudinal compression parallel to the line of flow of the fuel within the injector assembly. U.S. Pat. No. 5,752,487 discloses the use of a carbon dam disposed between the o-ring and the cylinder head, the function of which is to insulate the o-ring from excessive temperatures generated during conventional operation of the engine.
U.S. Pat. No. 6,412,471 discloses a throttle body system with an integrated electronic system for engine control and management. The engine shown and described in U.S. Pat. No. 6,412,471 is an internal combustion engine with a fuel injection system, by which fuel is injected directly into the inlet manifold of the engine. The flow of air to the engine is controlled using the throttle forming the subject of U.S. Pat. No. 6,412,471. The throttle comprises a passage for the flow of air, in which is located a movable throttle plate, by which the flow of air through the throttle is controlled. A mass air flow sensor is retained in a bore in the wall of the throttle body. The mass air flow sensor is sealed to the outer surface of the throttle body by an o-ring compressed between the mounting head of the sensor and the outer surface. The disclosure of U.S. Pat. No. 6,412,471 clearly indicates that the air flow through the throttle to the engine arises as a result of the induction stroke of the engine. Thus, the gas pressure generated within the throttle body is a partial vacuum, of the order generated in conventional, normally aspirated engines.
It has been found that fuel leaks can occur from the pressurized fuel supply system of certain fuel injected engines. In particular, it has been found that the high gas pressures required for the operation of the class of low-speed, two cycle gaseous fuel engines mentioned hereinbefore can give rise to gas leaks with conventional, known fuel supply systems. In particular, it has been found that the known sealing arrangements of throttle bodies used to control the flow of the pressurized gaseous fuel cannot maintain their integrity under the high pressures employed. This has led to fuel leaks occurring.
Accordingly, there is a need for an improved design of seals for pressurized normally gaseous fuel supply systems, in particular for the sealing of the throttle assembly used to control the flow of the gaseous fuel.